The present invention relates generally to foam-in-place materials. More particularly, the present invention relates to formulations and methods of making foamed synthetic polymers which exhibit enhanced mechanical properties, such as increased stiffness and rigidity in reinforcement application, improved adhesion to metallic substrates, and maintaining control over the reactive mixture and attendant foaming characteristics of the foam-in-place material.
Traditional foam-in-place structural materials known in the art generally disclose polyurethane materials and epoxy-based materials with or without a blowing agent. For example, commonly assigned U.S. Pat. No. 5,648,401 for Foamed Articles And Methods Of Making Same, which is hereby expressly incorporated by reference, teaches a three-ingredient foam-in-place structural material. Although these prior art materials are both useful and successful in a number of applications, certain structural reinforcement applications in the automotive industry require a material having improved mechanical properties, such as increased stiffness, improved adhesion to metallic substrates, and little reduction in modulus or glass temperature as exposure temperature is increased. In addition, specific reinforcement applications require a greater degree of control over the reactive mixture with potentially increased localized foaming in certain areas.
As known by those skilled in the art, a number of factors determine the suitability of a process for forming a foamed product of the type in which a blowing agent forms cells in a synthetic resin as the resin is cured. Most significantly, the interaction of the rate of cure and the rate at which the blowing gas is generated must be such that the correct foam volume is attained. If the resin cures too rapidly there is inadequate time for the gas to form the proper size and number of gas voids in the finished product. Over expansion of the forming foam product must also be avoided. Rapid expansion due to a slow cure rate may cause the expanding foam to simply collapse as a result of inadequate wall strength surrounding the individual gas cells.
Generally speaking, foamed products must have good stability when exposed to various environmental conditions and, most significantly, in many applications they must protect metal from corrosion when exposed to hostile environmental conditions. This is particularly true in automotive applications where the foamed product can be utilized and placed within portions of the vehicle that are routinely exposed to hostile environmental conditions, ambient temperature and weather fluctuations, as well as structural stress and strain.
In the past, many foamed parts were made using polyurethane which provides a number of desirable attributes. It is known, however, that alternatives to urethane-based or urea-based foams are frequently more environmentally desirable. Such environmental concerns relate to material handling during manufacturing as well as waste management concerns, in part due to unreacted functional groups in the finished products and difficulty in handling isocyanate functional chemicals in manufacturing processes.
Accordingly, there is a need in industry and manufacturing operations for a structural material which exhibits improved mechanical properties and which may be formulated to provide a directed and controlled reactive mixture to produce the foam-in-place material. The present invention addresses and overcomes the shortcomings found in the prior art by providing a first epoxy component formulated with a metal carbonate encapsulated by a polymer or thermoplastic shell or skin. A second component consisting of a strong acid is then combined with the first epoxy component in a reactive mixture to produce a foam-in-place material which demonstrates good adhesion to metallic substrates, resistance to high humidity or corrosive environments, and resistance to high temperature exposure when compared to other epoxy-based materials known in the art. In addition, the encapsulated metal carbonate core can serve to control and effect the reaction rate and characteristics of the reactive mixture as a function of the selected material, melting point, thickness, texture, particle size, and percentage by weight of the selected core as well as the percentage of acid used in the formulation.
The present invention relates to methods, materials, and products for foam-in-place materials. In one embodiment, the present invention comprises a two-component foam-in-place structural material for producing a foamed product. Though other resin systems are possible, the first component of the system includes an epoxy-based resin. Preferably, the first component is formulated with coated particles. Although the preferred particle is a metal salt, such a metal carbonate encapsulated within a wax, polymer, (e.g., Thermoset, thermoplastic, or mixture) a number of materials and encapsulation means may be used. In a preferred embodiment, a metal carbonate particle is encapsulated within a wax, shell or skin that will change state to expose the core to chemically react for initiating the production of gas for blowing. For example, the shell is a thermoplastic that, upon heating, will melt or soften to expose the surface of a metal carbonate core. It is contemplated that the thermoplastic shell having a metal carbonate core may further comprise a blowing agent formulated with or separately form the epoxy resin, and preferably used together as a first component. The second component is an acid that is capable of initiating polymerization of the resin. A reactive mixture is achieved through the combination of the first and second components wherein heat from the exothermic reaction of the acid with the epoxy component causes the thermoplastic shell, skin, or wax encapsulating a metal carbonate core to soften or melt thereby exposing the metal carbonate to the reactive mixture. The introduction of the acid with the metal carbonate-filled polymer particles results in a reaction between the metal carbonate and acid resulting in gas release. The resulting temperature achieved in the reactive mixture prior to particle exposure is somewhat dependent on the type of particle used to create the initial metal carbonate particle found in the epoxy as well as the type and characteristics of metal carbonate that is encapsulated within the thermoplastic shell, skin, or wax. It is contemplated that the reaction or reactive mixture of the epoxy component with the acid can be controlled and directed through the type, characteristics, and properties of the core selected to be encapsulated and formulated within the epoxy component. For example, the coating on the metal carbonate (for illustrative purposes, a metal carbonate) can have a varying melting point, or varying coating thickness. The percentage of metal carbonate in the formulation, size of metal carbonate particles, and percentage of acid strength and type of acid used in the formulation can be varied as well. All of these factors can effect the timing, characteristics, and foaming of the reactive mixture. As the homopolymerization exothermic reaction continues, the particles react and create gas thereby producing a foam-in-place material as the epoxy component cures.
The present invention provides a method of forming a foamed product which comprises the steps of combining the first component (e.g., with the metal carbonate core and meltable skin) with the second or acid component (which may, but not necessarily, comprise a curing agent depending upon the specific application). The first component, preferably an epoxy, is cross-linked through a polymerization reaction which advantageously may be catalyzed by the second component (e.g. the acid). In this regard, an exothermic reaction or reactive mixture is created between the epoxy component and the acid component when combined. The heat generated by the exothermic reaction softens the thermoplastic shell, skin, or wax encapsulating the configured core, or otherwise exposes the core to the acid. A gas releasing chemical reaction may then ensue. Thus, in one embodiment, as the thermoplastic shell with the metal carbonate core softens from the heat, gas is generated to create expansion. Simultaneously, a curing reaction occurs by the reaction of the epoxy component catalyzed by the acid component. In a preferred embodiment the mixture of materials is in liquid form. However, it is contemplated that the mixture of materials could also comprise a paste or solids of varying viscosities and textures.
In another aspect of the invention a foamed product is provided which comprises the steps of combining an epoxy resin component (formulated with the encapsulated core) with the acid component, which serves as the curing agent, and allowing the acid component formulation to cross-link the resin and react with the core formulated within the epoxy. It is contemplated that the exothermic reaction generated by the combination of the epoxy component formulation and the acid component formulation will enable the epoxy to react with the encapsulated metal carbonate to create a cell-forming gas thereby yielding the foam-in-place structural material.